PARK CITY – They are the voices in the chorus. That extra kick that turns a solid song into a massive hit. They are the background singers who transformed the music industry in the ’60s and ’70s often to the detriment of their own solo careers. Finally, these legendary artists step into the spotlight in Morgan Neville’s entertaining and enlightening documentary “Twenty Feet From Stardom” which premiered at the 2013 Sundance Film Festival on Thursday night.

Originally an idea of famed A&M Records chairman Gil Fiesen, “Twenty Feet” takes a sweeping look at the contributions of backup artists by using interviews with such famous faces as Bruce Springsteen, Sting, Bette Midler, Steve Wonder and Mick Jagger as well as first hand accounts from the forgotten voices themselves. The doc primarily focuses on Darlene Love, Merry Clayton and Lisa Fisher, famed backup singers who had varying degrees of success as solo artists. It also reflects, with a bit less detail, on Tata Vega (the real singing behind “Miss Celie’s Blues (Sister)” from “The Color Purple”) and Judith Hill (who was expected to be the breakout star of Michael Jackson’s “This Is It” tour). But Love, who was inducted into the Rock and Roll Hall of Fame in 2011, is the beginning and the end of this story.

No doubt deserving of a solo documentary in her own right, Love began her career as a member of the Blossoms, a singing trio that helped changed the sound of backup singers in the early ’60s. The group sang alongside artists such as Sam Cooke, Dionne Warwick and Elvis Presley, but just when they thought they would develop their own careers they were duped by producer Phil Spector. The “Wall of Sound” pioneer credited the Blossom’s work and Love’s lead vocals on two hits to another girl group, The Crystals. In fact, it was only the beginning of how Spector would continue to haunt Love’s career. Her attempts at a solo career were so hampered by contractual issues with Spector that she at one point resorted to cleaning homes for a living because it was her only way out. And no matter what her success since, Love is still best known for the Spector produced “Christmas (Baby Please Come Home).”

The middle portion of “Twenty Feet” shifts its focus to Merry Clayton a diva of a voice that any music fan would recognize from Lynyrd Skynyrd’s “Sweet Home Alabama” and the Rolling Stones‘ “Gimme Shelter.” Clayton got her first break as one of Ray Charles’ The Raelettes, but it was her backup work for Skynyrd and the Stones that fueled her own attempted solo career in the ’70s. Like Love, however, Clayton’s great material couldn’t find an audience. As one contributor notes, “It wasn’t fair, but there was one Aretha Franklin. One Diana Ross. There wasn’t room another.”

A few of the other background singers who reflect on the industry and their roles in music history include Claudia Lennear, Dr. Mable John and The Waters Family. Neville and editors Jason Zeldes, Kevin Klauber and Doug Blush had the unenviable task of weaving an unlimited well of anecdotes into a cohesive narrative while still allowing their “leading ladies” to remain the focus of the film. They are assisted in this endeavor by some nicely lit camerawork from Nicola B. Marsh and Graham Willoughby and the natural charisma and honesty of their subjects. Oh, and did we mention the singing?

Granted, some of the stories in “Twenty Feet” will be familiar to many music aficionados, but Neville’s use of archive tracks and rarely seen video footage is meshed with quick snippets of the ladies harmonizing to create a must-see historical documentary (and boy, they can still blow today’s “divas” away). Moreover, “Twenty Feet” accomplishes the rare feat of entertaining as it educates moviegoers that rock and pop music would be radically different without the contributions of these vocalists.

When “Twenty Feet” really breaks the conventions of a traditional music doc are the moments where its subjects send shivers up your arm with their incredible talent. One of the picture’s most memorable sequences is when Merry Clayton recalls how she was brought in to sing background on “Gimme Shelter” back in 1969. She was home in bed – pregnant – and gets a phone call asking her to come into the studio because the Rolling Stones needed someone to contribute to this new track they are working on. Jagger remembers Clayton arriving in her pajamas and curlers (Clayton says she had a scarf over them) hoping this would work out. Clayton records the now famous line “Rape and murder. It’s just a shout away. It’s just a shout away.” On the second take, however, she decides to really “blow it out.” Neville then plays that isolated track of Clayton singing while recording both her and Jagger’s reaction to it present day. Jagger tries to keep his cool, but when Clayton’s stunning solo hits its crescendo he just can’t help breaking out into a huge grin. And neither will most audiences. It’s just one reason why Clayton is a living legend.

To be fair, “Twenty Feet” does suffer slightly from repeating its themes a few too many times and the inclusion of contemporary backup singer/struggling solo artist Hill feels a bit unnecessary. The rest of the film more than makes up for these minor shortcomings, however.

Music documentaries can be hard sells even in the art house circuit, but a smart mini-major such as Sony Classics or Roadside Attractions could easily mine word of mouth to a gross similar to 2009’s “It Might Get Loud” or even “Searching For Sugar Man.”